A large amount of new content is published across the Internet every day. This content includes, for example, news articles, blog entries, and social media posts, among others. The content owners or other authorized parties often configure their websites or applications to present advertisements in association with published content, such as by presenting a banner advertisement or other advertisement on a webpage that also includes the article or other primary content. These advertisements may be selected dynamically at the time that the content is presented for display to a given user. Advertising services (which may include an advertising network that connects advertisers with publishers or other website operators) may employ an automated process, such as contextual advertising or contextual targeting techniques, to select an advertisement in a given instance that is relevant to the page on which the advertisement will appear. For example, a contextual advertising system may scan the text of a website for the presence of any keywords previously established by an operator of the advertising system, then may return an advertisement based on the identified keywords. In a sample instance, if a user views a website that includes words that a contextual advertising system has previously associated with basketball, the user may see advertisements for basketball-related companies.